The present invention relates broadly to an electronic countermeasures apparatus, and in particular to an angle set-on apparatus for determining and jamming a hostile radar emitter.
The present trend in electronic countermeasures pods is toward power managed systems which are equipped with a receiver/processor unit. The receiver/processor serves to identify emitters and, where appropriate, assigns PRI trackers to the received pulse trains. A major function of the PRI tracker is to provide time-of-arrival windows to the jammer unit that surrounds the expected arrival time of a hostile emitter pulse. Typically, a time-of-arrival window has a duration of from 1 to 16 .mu.secs. The presence of a tracker time-of-arrival window allows the jammer unit to modify techniques and parameters for the duration of the window to achieve optimum effectiveness against the received pulse train that are being tracked. By employing multiple tracker units, it is possible to time share the available jamming unit resources against the multiple pulse trains and, thereby, to provide system power management in the time domain. The present receiver/processors are also capable of providing power management in the frequency set-on (FSO) mode. In this technique the receiver/processor, after identifying the emitter, centers the received signal in its IF bandpass. It then samples the center frequency of the jammers noise transmission and, by indirect commands, proceeds to vary the jamming center frequency until it too is centered in the receiver/processor's IF bandpass. Using the frequency set-on technique, the receiver/processor can typically place the noise jamming center frequency to within .+-.2 MHz of the received emitter frequency. It is important to note that the absolute frequency accuracy or the receiver/processor or the jammer noise source is unimportant in that both are centered around the received emitter frequency.
The present electronic countermeasure pods are equipped with receiver/processors that perform power management in the time and frequency domains. However, future systems which are equipped with receiver/processor units can be expected to continue to provide time and frequency domain power management and to provide a spatial or angle-of-arrival power management capability. The spatial power mangement technique of using phased arrays will permit the jammer unit 10 to increase its effective radiated power by narrowing its transmit antenna beam around the emitters angle of arrival. The major obstacle to providing a spatial domain power mangement capability in an electronic countermeasure pod is the limited packaging space available.
In a pod application, a typical phased array installation may have eight transmit elements of which each one may have its own low power traveling wave tube amplifier that is driven from a matrix switching lens or beam forming network. In addition, in most conventional approaches, a direction finding system is generally utilized to point the phased array. These requirements increase both the packaging volume and the implementation costs. The problems that are normally associated with pointing a phased array, are aggrevated further by the antenna pattern distortion which can occur in a pod installation. In addition, a further problem exists with conventional phased arrays in that they can only provide on an instantaneous basis either omni or narrow beam coverage, but not both. This limited operation would entail the loss of required continuous coverage every time the beam was narrowed around a particular emitter's angle of arrival. However, this problem has been solved by the development of a dual mode phased array antenna that provides both simultaneous omni and narrow beam coverage. This relatively simple array can be implemented using either the conventional approach of multiple low power traveling wave tube amplifiers or using a single high power traveling wave tube as the drive source. The latter is of importance in that it makes possible a low cost retrofit into existing pod transmitters.